Synthesis, crystallographic and theoretical studies of the new Zintl phases Ba2Cd2Pn3 (Pn = As, Sb), and the solid solutions (Ba(1-x)Sr(x))2Cd2Sb3 and Ba2Cd2(Sb(1-x)As(x))3.

Two new Zintl compounds Ba(2)Cd(2)As(3) and Ba(2)Cd(2)Sb(3) have been synthesized and structurally characterized. They crystallize in a novel monoclinic structure type with the space group C2/m (no. 12), featuring polyanionic layers made of CdPn(4) tetrahedra (Pn = As, Sb) and homoatomic Pn-Pn bonds. The topological relationships between the structure of Ba(2)Cd(2)Sb(3) and those of BaCd(2)Sb(2) (CaAl(2)Si(2) type) and Ba(3)Cd(2)Sb(4) (own type) are discussed as well. Based on electronic structures calculations, carried out by the density-functional method, and resistivity measurements, pure Ba(2)Cd(2)As(3) is shown to be a small-gap semiconductor and pure Ba(2)Cd(2)Sb(3) to be a poor metal. The structures of the title compounds are amenable to doping on both cation and pnicogen sites, which could enable fine-tuning the transport properties, and make them promising materials for thermoelectric applications.